We had some plaster of paris left over from making the sidewalk chalks, and tried casting small objects using it. The play dough we used as moulds was also homemade. We added a little bit of olive oil on the surface before pressing the toys and seashells on the dough, which reduced the stickiness.

You need a tiny amount of the plaster and I prepared a bit too much of it, so I poured the rest of it into number shaped silicone moulds.